Electronic cameras are generally divided into two broad categories: still cameras and video cameras. However, there is a degree of overlap between the two types of camera. For example, some “video” cameras are capable of capturing both movies and still images.
On the other hand, some still cameras are provided with a “movie” or “video” function, which allows the camera to capture a sequence of images. These images can subsequently be shown as a movie. This invention is concerned primarily (but not exclusively) with the latter type of camera.
Electronic cameras generally include an image capture device or sensor having an array of photosensitive detectors or picture elements (pixels). A moving image or movie can be captured by recording a sequence of images detected by the sensor.
The rate at which a sequence of images can be captured (the frame rate) depends in part on the size of the sensor (that is, the number of pixels in the array), and is limited by the rate at which data can be read (digitised) from the sensor. Reading information from an imaging sensor at high speed introduces noise (read noise), which lowers the signal quality of the image. Accordingly, if the sensor has a large number of pixels, the frame rate will generally be rather slow. Smaller sensors with fewer pixels may provide a higher frame rate, but the resolution of the image will be correspondingly reduced.
The inventor's previous patent application WO 2008/138543A describes an image capture device including a sensor with an active area comprising a plurality of pixels, and a shutter array comprising a plurality of shutter elements that can be activated individually to control the exposure of the individual pixels. The pixels are arranged in a number of pixel subsets that can be exposed sequentially to capture a sequence of lo-res images each comprising less than the full set of pixels, or simultaneously to capture a hi-res image comprising all or substantially all of the pixels. However, the provision of a separate shutter array adds to the size and complexity of the device.
It is an object of the present invention to provide an image sensor and a method of capturing images that mitigate at least some of the aforesaid disadvantages.
According to one aspect of the invention there is provided an image sensor having a plurality of pixels arranged in an array, a selection means for selecting individual pixels in the array, and shutter control means for transmitting a shutter signal to the pixels, wherein each said pixel is constructed and arranged to sense incident light only when both selected and in receipt of a shutter signal, whereby pixels in said array can be triggered individually to capture light at different times.